1. Field of the Invention
The present invention relates to a circuit for driving an AC plasma display panel at a low power, and more particularly, to an energy recovery sustain circuit for an AC plasma display panel.
2. Discussion of the Related Art
The AC plasma display panel is in general one of luminous device which uses gaseous discharge within each discharge cell for displaying an image. Because the AC plasma display panel is simple to fabricate, easy to fabricate a large sized screen, and fast in response, it is spot lighted as a direct view image display with a large screen, particularly as a display directed to an age of HDTV.
The AC plasma display panel, provided with electrodes, a dielectric layer and a discharge gas, acts as a load capacitor which charges and discharges for itself. However, the large power consumption in driving the AC plasma display panel, i.e., in the charging and discharging of the load capacitor, particularly, when the size is greater, has been a great obstacle for making this AC plasma display panel popular. Accordingly, instead of a general sustain circuit, use of an energy recovery sustain circuit for sustained driving of the panel is suggested, for pursuing a low power consumption of a driving circuit which drives the AC plasma display panel. The energy recovery sustain circuit is a circuit provided with an inductor which forms an LC resonance circuit with a load capacitor in the panel for recovery and temporary storage of an energy lost during discharge of the load capacitor and supplying the energy for the next time charging of the load capacitor, thereby reducing an energy loss in the sustained driving of the panel.
FIG. 1 illustrates a typical type energy recovery sustain circuit, one of background art energy recovery sustain circuit, provided with a system including first and second energy recovery sustain driving parts 10 and 20 of identical systems, for supplying sustain pulses of a V.sub.o voltage to a load capacitor C.sub.L in the AC plasma display panel. Each of the first and second energy recovery sustain driving parts 10 and 20 is provided with an output terminal OUT connected to the load capacitor C.sub.L, an inductor L0 having one end connected to the load capacitor C.sub.L through the output terminal OUT to form a resonance circuit, a capacitor C1 having a capacitance greater than the load capacitor C.sub.L and one end grounded for charging and discharging Vo/2 voltage thereto/therefrom, capacitor discharging means 11 connected to the other end of the capacitor C1 and the other end of the inductor L0 for discharging the Vo/2 voltage charged in the capacitor C1 so as to charge the load capacitor C.sub.L from 0 to Vo, first voltage sustaining means 12 connected to the output terminal OUT for sustaining voltages V.sub.L on both sides of the load capacitor C.sub.L to Vo when the load capacitor C.sub.L is charged to Vo voltage, capacitor charging means 13 connected between the other end of the capacitor C1 and the other end of the inductor L0 for discharging the Vo voltage charged in the load capacitor C.sub.L down to 0 voltage to charge the capacitor C1 up to Vo/2 voltage, and second voltage sustaining means 14 connected to the output terminal OUT for sustaining a voltage V.sub.L on both sides of the load capacitor C.sub.L at 0 when the load capacitor C.sub.L is discharged down to 0 voltage. The capacitor discharging means 11 is provided with first switching means Q1 having one end connected to the other end of the capacitor C1 for being at turned on while the load capacitor C.sub.L is charged from 0 to Vo voltage, and a first diode D1 having an anode connected to the other end of the first switching means Q1 and a cathode connected to the other end of the inductor L0 for receiving a current I.sub.L discharged from the capacitor C1 through the first switching means Q1 and providing to the inductor L0 while the first switching means Q1 is at turned on. The capacitor charging means 13 is provided with second switching means Q2 having one end connected to the other end of the capacitor C1 for being at turned on while the load capacitor C.sub.L is discharged from Vo to 0 voltage, and a second diode D2 having a cathode connected to the other end of the second switching means Q2 and an anode connected to the other end of the inductor L0 for receiving a current -I.sub.L discharged from the load capacitor C.sub.L through the inductor L0 and providing to the second switching means Q2 while the first switching means Q1 is at turned on. The first voltage sustaining means 12 is provided with a third diode D3 having a cathode connected both to a Vo power source and the output terminal OUT, and third switching means Q3 having one end connected an anode of the third diode D3 and the other end connected to the Vo power source for being turned on when the load capacitor C.sub.L is charged from 0 to Vo voltage. The second voltage sustaining means 14 is provided with a fourth diode D4 having an anode connected to the output terminal OUT, and fourth switching means Q4 having one end connected to a cathode of the fourth diode D4 and the other end grounded for being turned on when the load capacitor C.sub.L is discharged from Vo to 0 voltage.
The operation of charging and discharging of the aforementioned typical type energy recovery sustain circuit will be explained with reference to FIGS. 2a.about.2f. FIG. 2a illustrates a waveform of a voltage V.sub.OUT at the output terminal OUT, FIG. 2b illustrates a waveform of a current I.sub.L flowing through the inductor L0, and FIGS. 2c.about.2f illustrate switching timings of the first to fourth switching means Q1, Q2, Q3 and Q4 related to the above waveforms.
In the typical type energy recovery sustain circuit, when the entire system is turned on initially to occur many times of continuous discharges at the load capacitor C.sub.L, a current of discharge flows from the load capacitor C.sub.L to respective capacitor C1 through the inductors L0 of the first, and second energy recovery sustain driving part 10 and 20, to charge to respective capacitors C1 a Vo/2 volt. When a Vo/2 volt is charged in each of the capacitors C1 of the first, and second recovery sustain driving parts 10 and 20, periodic charging and discharging is occurred between the typical energy recovery sustain circuit and the load capacitor C.sub.L at proper intervals, making the energy recovery sustain drive for the AC plasma display panel. In this instance, the discharge in the load capacitor C.sub.L is a sustain discharge for the AC plasma display panel. One cycle of the periodic charging and discharging between the typical energy recovery sustain circuit and the load capacitor C.sub.L has four intervals, operations in each of which are different from one another.
&lt;T1 INTERVAL&gt;
In the T1 interval, the capacitors C1 of the first, and second energy recovery sustain driving parts 10 and 20 are discharged to charge the load capacitors C.sub.L with the discharge energies. As shown in FIG. 2c, in this T1 interval, only the first switching means Q1 in the first, and second energy recovery sustain driving parts 10 and 20 are turned on, while the rest switching means Q2, Q3 and Q4 are left turned off as shown in FIGS. 2d.about.2f. When the first switching means Q1 in the first, and second energy recovery sustain driving parts 10 and 20 are turned on, the Vo/2 volt charged in respective capacitors C1 are discharged, to flow a discharge current I.sub.L caused by the Vo/2 to the load capacitors C.sub.L through the first switching means Q1, the first diodes D1 and inductors L0. At the end, as shown in FIG. 2a, the load capacitors C.sub.L are charged up to Vo volt in T1 interval by the discharge current I.sub.L from the first, and second energy recovery sustain driving parts 10 and 20, respectively. Accordingly, as shown in FIG. 2a, in this interval, a waveform rising from 0 to Vo, i.e., a rising section of the sustain pulse is shown at the output terminal OUT.
&lt;T2 INTERVAL&gt;
In the T2 interval after the T1 interval, voltages V.sub.L at both ends of the load capacitor C.sub.L is sustained at Vo, to charge the Vo volt to the load capacitors C.sub.L, continuously. As shown in FIG. 2e, in this T2 interval, only the third switching means Q3 in the first, and second energy recovery sustain driving parts 10 and 20 are turned on, while the rest switching means Q1, Q2 and Q4 are left turned off as shown in FIGS. 2c, 2d and 2f. When the third switching means Q3 in the first, and second energy recovery sustain driving parts 10 and 20 are turned on, a voltage from the Vo power source is provided to the output terminal OUT through the third switching means Q3 and the third diode D3. As a result, as shown in FIG. 2a, the Vo volt is continuously charged to the load capacitors C.sub.L. That is, since the voltage V1 at both ends of the capacitor C1 is lower than the voltage V.sub.L at both ends of the load capacitor C.sub.L in this T2 interval, as shown in FIG. 2b, no discharge current I.sub.L flows through the inductor L0. Therefore, for continuous charging to the load capacitors C.sub.L, it is necessary to provide the Vo volt to the output terminal OUT. Accordingly, as shown in FIG. 2a, in the T2 interval, a waveform held at the Vo volt, i.e., a sustained section of the sustain pulse is shown at the output terminal OUT.
&lt;T3 INTERVAL&gt;
In the T3 interval after the T2 interval, energies discharged from the load capacitors C.sub.L are charged in the capacitors C1 in the first and second energy recovery sustain driving parts 10 and 20, respectively. As shown in FIG. 2d, in this T3 interval, only the second switching means Q2 in the first, and second energy recovery sustain driving parts 10 and 20 are turned on, while the rest switching means Q1, Q3 and Q4 are left turned off as shown in FIGS. 2c, 2e and 2f When the second switching means Q2 in the first, and second energy recovery sustain driving parts 10 and 20 are turned on, Vo volts charged in the load capacitors C.sub.L are discharged. Therefore, as shown in FIG. 2b, a discharge current -I.sub.L flows to the capacitors C1 through the second switching means Q2 via the inductors L0 and second diodes D2 in the first, and second energy recovery sustain driving parts 10 and 20. As a result, during the T3 interval, the capacitors C1 are charged of Vo/2 volts by the discharge current -I.sub.L from the load capacitors C.sub.L. Therefore, as shown in FIG. 2a, in the T3 interval, a waveform falling from Vo to 0, i.e., a falling section of the sustain pulse is shown at the output terminal OUT.
&lt;T4 INTERVAL&gt;
In the T4 interval after the T3 interval, voltages V.sub.L at both ends of the load capacitors C.sub.L are sustained at 0. As shown in FIG. 2f, in this T4 interval, only the fourth switching means Q4 in the first, and second energy recovery sustain driving parts 10 and 20 are turned on, while the rest switching means Q1, Q2 and Q3 are left turned off as shown in FIGS. 2c.about.2e. When the fourth switching means Q4 in the first, and second energy recovery sustain driving parts 10 and 20 are turned on, the voltage at the output terminal OUT is sustained at 0 by the second voltage sustaining means 14 as shown in FIG. 2a. As a result, voltages V.sub.L at both ends of the load capacitors C.sub.L are sustained at 0. In this instance, the voltages V.sub.L at both ends of the load capacitors C.sub.L are lower than the voltages V1 at both ends of the capacitors C1 in the first, and second energy recovery sustain driving parts 10 and 20, causing no discharge current -I.sub.L flow through the inductors L0. In this instance, the voltages V.sub.L at both sides of the load capacitors C.sub.L are lower than the voltages V1 at both sides of the capacitors C1 in the first, and second energy recovery sustain driving parts 10 and 20, causing no discharge current -I.sub.L flow through the inductors L0. Therefore, as shown in FIG. 2a, in the T4 interval, a waveform held at 0 volt, i.e., a sustained 0 volt section of the sustain pulse is shown at the output terminal OUT.
A basic form of the sustain pulse provided to the load capacitors C.sub.L in the AC plasma display panel during T1 to T4 are rectangular the same as the waveform of voltage Vout at the output terminal OUT shown in FIG. 2a. The waveforms of a current I.sub.L of the rising section(T1 interval) and of the falling section(T3 interval) in the sustain pulse shown in FIG. 2b are segments of a sinusoidal wave of a resonant oscillation of which frequency is determined by an inductance of the inductor L0, a capacitance of the load capacitor C.sub.L, and a capacitance of the capacitor C1. It is apparent that, if the capacitor C1 is provided to a sustain circuit for temporary storage of a discharge energy from the load capacitor C.sub.L and supplying the discharge energy as a charging energy to the load capacitor C.sub.L in the next cycle, there is reduction in an energy loss with reduction of power consumption compared to a sustain circuit without the energy recovery. For example, while a power consumption of a current sustain circuit operative at a frequency f.sub.0 without the energy recovery is P=C.sub.L Vo.sup.2 f.sub.0 during generation of sustain pulses, a power consumption of the typical type energy recovery sustain circuit is P=C.sub.L (Vo/2).sup.2 f.sub.0 during generation of sustain pulses, where C.sub.L is a capacitance of a load capacitor, Vo is a sustain driving voltage and f.sub.0 is an operating frequency. Therefore, it can be known that the typical type energy recovery sustain circuit has a power consumption smaller than the current sustain circuit.
However, even if the background art typical type energy recovery sustain circuit reduces a power consumption of a panel driving circuit by the energy recovery action of the circuit, a capacitance of the panel still increases as the panel size increases. In the background art circuit, obtaining a maximum energy recovery efficiency is difficult in a case when a timing of recovery and a screen luminance of the panel are changed(i.e., when a number of on/off cells are different) due to difficulty in finding a maximum resonance point, causing much more power consumption in driving the panel, with subsequent increase of expenses, to require a method for reducing the power consumption.